Abstract More than 230,000 women will undergo surgery for breast cancer in 2012 in the US. Of these, around 75% will be candidates and choose breast conserving surgery (BCS). BCS is cosmetically preferable to the alternative (mastectomy) and long-term survival rates are equivalent. But BCS has the potential to be significantly more expensive. Of the 175,000 women who undergo BCS, 25%-40% will be recalled to the hospital for additional surgery to remove active cancerous tissue that was not detected and removed during the first procedure. Apart from the negative impact on patients, which is the primary concern of clinicians, second surgeries have a significant economic impact on healthcare costs in general as well as on individual provider institutions. The current gold standard for the detection of active tumor margins after tumor excision is FFPE (Formalin-Fixed, Paraffin-Embedded) tissue pathology. Tissue removed by the surgeon is evaluated for active tumor margins after the patient is discharged and results may take up to two weeks. Because it is not performed intra-operatively, FFPE virtually guarantees there will be second surgeries when active margins are detected. More importantly, FFPE does not examine the entire excised tumor, but only a number of frozen sections. The inevitable sampling errors may miss active tumor spikes. Data suggests that approximately 15% of patients that are declared to have clean margins have local recurrence within a year indicating that pathology missed disease in the margins, likely due to undersampling. Recently, The New York Times reported on surgical breast cancer treatments in the USA further underscoring that an unmet public need, the reduction in second surgeries due to undetected/unexcised cancer cells in tumor margins, clearly exists (Breast Cancer Surgery Rules Are Called Unclear, NY Times, page A1, February 1, 2012). A recent survey revealed that only 48% of the 351 American surgeons who responded grossly examine margins intraoperatively with a pathologist and even fewer used any techniques during the surgery to determine if they had removed all the cancer tissue from the breast. Out of all the participating surgeons, 28% would consider a 1-mm margin free of cancer as negative, 50% a 2-mm margin, 12% a 5- mm margin and 3% a 10-mm margin. Clearly, these shortcoming define an unmet clinical need for BCS. Solution to the Unmet Need. Molecular imaging is a relatively new field that tries to identify cells by imaging them based on differences in their biochemistry rather than trying to resolve subtle anatomical differences that are used to identify cancer in typical X-ray or mammography exams. For a number of years our laboratory has been looking into the possibility of using quenched molecular imaging probes and application technologies to rapidly identify cancer cells in the body. Recently, we have developed novel techniques to apply molecular probes topically to tissues and very rapidly differentiate cancer cells from normal tissues. Our idea is to utilize this novel technology pioneered in our laboratories to develop a standardized method to reduce re-excisions and false negatives for BCS patients. Exploiting increased protease expression at the edge of breast cancers this proposal introduces the novel concept of ex vivo topical administration of quenched molecular imaging probes to identify cancer. Minutes after application, limited diffusion of the probe into lumpectomy specimens defines a margin and allows identification of infiltrating cancer cells without a requirement for vascularization. This approach enables rapid and global identification of cancer presence both on the surface and in the margins of resected specimens during surgery, all of which is unique to this technology. If successful this technology could reduce the number of re-excisions by up to 60%. Moreover, if will reduce re-excisions and the false negative rate that results from undersampling during histopathological analysis. The research proposed here will first optimize the probe mixtures for this procedure and then will test the technology in the lumpectomy specimens of 50 women. The results of this study will statistically test this technology. Since all of the procedures happen outside of the body, there are minimal regulatory hurdles to drive this technology rapidly into the hands of surgeons.